The content of a person's breath may indicate how susceptible they are to weight gain, according to a recent study accepted for publication in The Endocrine Society's Journal of Clinical Endocrinology & Metabolism (JCEM). People whose breath has high concentrations of both hydrogen and methane gases are more likely to have a higher body mass index and percentage of body fat, according to the findings. The combination of the two gases signals the presence of a microorganism that may contribute to obesity.